The present invention relates to a solid-state imaging device having a multi-layered scanning circuit and photoconductive film formed on a semiconductor substrate.
In order to obtain a high photosensitivity, a conventional solid-state imaging device with a multilayered structure employs a photoconductive film of amorphous silicon formed on a scanning circuit substrate of either the MOS, CCD or BBD type. One problem with this structure is the high possibility of defects such as voids or cracks developing in the amorphous silicon film where steps occur at the electrode edges or contact holes in the substrate. If any of these defects remain unremoved after the photoconductive film is separated into individual picture elements (pixels), the areas that correspond to such defects are selectively etched faster than the other areas or leakage currents will flow in the residual defects, thereby causing considerable degradation of the device characteristics.
In order to prevent the occurrence of such defects, a substrate having a very high degree of surface flatness must be used. However, this requires highly sophisticated production techniques and results in a higher cost because of the increased number of process steps.
The thin amorphous silicon film is usually formed by a plasma-assisted CVD technique using glow discharge. Dust particles or other foreign material in the CVD equipment often cause pinholes and other defects in the amorphous silicon film and introduce nonuniformities in the quality of the film, not only with respect to a single wafer, but also between individual wafers. These problems taken together present a barrier against the manufacturing of solid-state imaging devices of the multi-layered structure with higher yields.